1. Field: The field of the invention is devices for preparing the snow of ski runs.
2. State of the Art: A large family of vehicle drawn implements for preparing the snow of ski runs have been developed. Principally, these include snow "tillers" having a rotating bar covered with radial snow-cutting teeth which chop, stir, and loosen the snow. Plow blades are of course used to reduce major hillocks, generally redistribute the snow across the run, fill large hollows and even move snow onto the run from neighboring areas. "Powder makers" generally employing perforated drums drawn rotatably over the snow, reduce surface lump snow to more true powder-like form. The remaining principal implement is called a snow "compactor". It is intended to consolidate snow upon the run, and to smooth and fill relatively minor hillocks and depressions to produce a generally compacted snow base upon the run, being however sufficiently loose upon the surface for enjoyable, relatively effortless skiing. Many other approaches to snow surface preparation have on occasion been used, although the above are the principal implements currently in use. These include agricultural type harrows and disks. Heavy bars or rollers have simply been dragged sideways along the run, as have even weighted canvases, and sections of chain-link fence. The canvas may have been the first utililization of a flexible sheet for snow surface treatment, but flexible elements are not uncomon. The above mentioned tiller, for example, typically employs a hood with a skirt with a narrow flexible resilient trailing member attached to its lowermost edge, with a rubberoid comb attached to ride resiliently upon the snow, responding to local variations in elevation of the snow surface. The elongate resilient member with comb is actually a compactor bar acting behind the tiller cutter bar upon the loose, rough snow created by the cutter bar. The tiller also typically utilizes flexible wings at the end of the cutter bars, which flexibly contact the snow to provide smooth transitions from the tilled path to the neighboring snow paths, each another flexible compactor bar, even if only a short one.
However, most prior art snow compactors are separate implements comprising a rigid elongate bar with a curved snow-contacting bottom wall. The compactor bars are typically mounted to swivel upon the vehicle tow mechanism so that some adjustment is provided to transverse variation in snow path contour. Some of these bars operate essentially under their own weight, while others are additionally pressed positively downward upon the snow with greater or less force by hydraulic cylinders or the like. Some have remotely controlled tilting mechanisms to adjust the angle between the compacting surface and the snow. These snow-compacting devices are unnecessarily heavy, restricting their usefullness especially on steep slopes. Because they are rigid and massive, they often do not adjust rapidly to variations in the snow surface, and therefore leave such surfaces less than smooth, and may be locally damaged by rocks and the like.
Some of these prior art rigid compactor bars also incorporate narrow flexible extensions of their trailing edges, to compensate somewhat for the above deficiencies. These flexible extension members are only a few inches wide and extend the full length of the bar, and generally incorporate a comb or the like at their trailing edge. Thus, the use of flexible snow-contacting members is also not new even with independent compactor units. See prior art FIG. 7. These prior art flexible members have been of sheet plastic and the like, conveyor type belting generally being utilized. While definitely flexible, they are also definitely resilient, and are stiff enough to bear positively, rather than limply, as canvas might, upon the snow.
Another snow path preparation implement comprises a lightweight plastic snow-contacting blade, essentially planar when not stressed. The leading edge of the blade is connected to an elongate rigid metallic bar, which is in turn secured to the vehicle towing mechanism. It is believed that the angle of attack of the blade with the snow may be adjusted prior to use, but that no remote control of blade angle is provided.
The blade is flexible and resilient, and curves substantially when it is drawn over the snow under its own weight, or under the urging of motors forcing the towing mechanism downward. The plastic compactor blade is essentially of constant section from trailing edge to leading edge, so that the curve is greatest at the leading portion near the rigid connecting member, and less pronounced over the trailing portion. Because of the limited elastic range and low elastic modulus typical of plastics, the blade must be quite thick and rigid to assure that neither the operating stress nor strain exceed the limits of the material. This not only limits the flexure of the blade lateral to its length, but also the local longitudinal or biaxial flexure of the trailing portion of the blade in response to irregularities in the snow surface. The elastic modulus and strain capability is sensitive to temperature, so that both flexibility and strength vary markedly with weather conditions. Also, the high elastic hysteresis and low fatigue resistance are not desirable where long operating life without permanent distortion or fracture is desired.